Primate Preferences

Monday, March 2, 2020

by Lincoln Park Zoo

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Lincoln Park Zoo

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Everyone has a preference, whether it concerns a favorite sports team or the optimal route to work. Some of the earliest preferences we form are connected to food – what tastes good, is filling, or simply the most fun to eat. Non-human primates also have preferred foods and, given that we know they like to work – such as foraging or using tools- for their preferred foods, we wanted to develop a quick and reliable way to test the food preferences of the primates at Lincoln Park Zoo.

If you have visited Lincoln Park Zoo, chances are you have seen one of the cognitive research demonstrations, in which members of the Lester E. Fisher Center for the Study and Conservation of Apes give the Japanese macaques, western lowland gorillas, and chimpanzees the opportunity to complete puzzles on touchscreens. These studies are voluntary, and the animals choose whether to participate or not. Knowing all this, would we be able to use the touchscreens to test the primates’ food preferences?

To answer this, we showed the primates photos of four foods on a touchscreen computer to see which they would choose. First, we showed the macaques and apes one photograph at a time, teaching them that when they press the photo on the touchscreen they receive that same food. Next, we showed them pairs of photographs to choose between and whichever food the macaques and apes selected, we would give them. Using their choices over multiple pairings, we calculated each primate’s relative food preferences. For instance, Mito, one of the macaques, picked peanut as her most-preferred food, with jungle pellet (a special cracker that macaques sometimes receive in their diets) in second place, and carrot and celery tied for last place.

More recently, we have added new foods to the mix to test the primates’ preferences on an expanded array of foods. From this work, we have discovered that while there were differences between individuals in the order of their food preferences, they were consistent over time in their preferences. For example, chimpanzee Cashew preferred grape over all other options, even when we increased the number of options she could choose from. In contrast, gorilla Mosi selected many foods at equal rates, suggesting he does not have strong preferences or dislikes. Importantly, we also discovered, through careful evaluation of the primates’ responses, that they spontaneously recognized the foods shown in the photographs. This suggests that, in the future, we can show the primates photos of other items to test their preferences of non-food items, such as environmental enrichment.

This may seem like a lot of work to figure out what foods the primates at the zoo like best, but our study has further-reaching applications. First, we showed that it is possible to evaluate many primates in a short amount of time using touchscreens (we worked with 18 monkeys and apes). Second, our study also provided the primates with the opportunity to make choices, which is crucial to promoting positive welfare and mental stimulation. As they encounter new tasks and decision-making opportunities, the macaques and apes always have a chance to keep their brains active. Lastly, the results of this study can help animal care staff tailor their care to each individual animal. For instance, animal care staff could provide gorilla Kwan with his most-preferred food (tomato!) as a reward after completing an operant training session. Conducting multifaceted studies like this are one of the ways Lincoln Park Zoo uses science to inform care and enhance welfare.

The above graph depicts the relative preferences of various gorillas. The higher the worth value, the more the individual likes the food item.

More detailed results from this comparative study can be found in the International Journal of Primatology. This article was authored by myself; former research assistants Crystal Egelkamp and Sarah Jacobson; Steve Ross, PhD, Director of the Lester E. Fisher Center for the Study and Conservation of Apes; and Lydia Hopper, PhD, Assistant Director of the Fisher Center.